分光光度法测定铀的影响因素分析

显色剂偶氮砷Ⅲ与铀酰离子 $ \left(\mathrm{UO}_{2}^{2+}\right) $的络合作用是建立分光光度法测定铀的理论基础, 测试过程中的pH值、酸介质、温度、干扰离子等是影响其精确性的主要因素。文章研究了上述因素对偶氮砷Ⅲ-分光光度法测定铀的影响。结果发现: pH值对偶氮砷Ⅲ- $ UO_{2}^{2+} $溶液在652 nm波长处吸光度的影响非常明显, pH=2.5时吸光度最高, 可达0.59, 而当pH=1.0或pH=5.0时其吸光度仅为0.09; HCl、 $ HNO_{3} $、 $ H_{2}SO_{4} $均适宜作为介质用于分光光度法测试铀质量浓度, 且pH值最佳范围为2.0~3.0; 由于温度升高增加了 $ UO_{2}^{2+} $的水解能力, 使其与偶氮砷Ⅲ形成络合物的能力减弱, 从而导致测定的吸光度会有所下降, 因此同批次实验应在相同环境和温度下进行; EDTA螯合剂能有效抑制各种二价、三价金属离子对测试的干扰, 而四价的 $ Th^{4+} $在较低酸度下易水解, 因此通过调节pH值可规避其对铀测试的影响。测试结果表明, 在优化条件下偶氮砷Ⅲ- $ UO_{2}^{2+} $溶液在652 nm波长处吸光度与铀质量浓度呈现良好的线性关系 $ \left(\mathrm{R}^{2}=0.999\mathrm{~1}\right) $, 表观摩尔吸光系数为 $ 5.45\times10^{4}\mathrm{~L}/(\mathrm{mol}\cdot\mathrm{cm}) $, 表明该条件下通过分光光度法可对铀进行精确定量分析。

The complex interaction between arsenazo III chromogenic agent and uranyl ion $ (\mathrm{UO}_{2}^{2+}) $ is the theoretical basis for the determination of uranium by spectrophotometry. The pH value, acid medium, temperature and interfering ions during the testing process are the main factors affecting its accuracy. The effects of these factors on the determination of uranium by arsenazo III-spectrophotometry were studied. The results showed that the effect of pH value on the absorbance of arsenazo III- $ UO_{2}^{2+} $ solution at the wavelength of 652 nm was very obvious. At pH 2.5, the absorbance value reached a maximum of 0.59, whereas at pH 1.0 or 5.0, it was only 0.09. HCl, $ HNO_{3} $, and $ H_{2}SO_{4} $ are suitable media for spectrophotometric determination of uranium content, with the optimal pH range being 2.0–3.0. Due to the increased hydrolysis capacity of $ UO_{2}^{2+} $ with the increase of temperature, its ability to form complex with arsenazo III is weakened, resulting in a decrease in the measured absorbance value. Therefore, the same batch of experiments should be carried out under the same environment and temperature. EDTA chelating agent can effectively inhibit the interference of various bivalent and trivalent metal ions on the test, and the tetravalent $ Th^{4+} $ can be easily hydrolyzed under low acidity, so its influence on uranium test can be avoided by adjusting the pH value. Under optimized conditions, the absorbance of arsenazol- $ UO_{2}^{2+} $ solution at 652 nm showed a good linear relationship with the concentration of uranium( $ R^{2}=0.999\ 1 $), and the apparent molar absorbance coefficient was $ 5.45\times10^{4}\ \mathrm{L}/(\mathrm{mol}\cdot\mathrm{cm}) $, indicating that uranium could be accurately quantified by spectrophotometry under these conditions.